But many nutrients are also lost when patients undergo these surgeries, senior study author Dr. Kuo-Chin Huang of the College of Medicine at National Taiwan University in Taipei told Reuters Health.

“The commonly lost nutrients are vitamin D and calcium, which are related to the development of osteoporosis,” Huang said by email. “And maybe there are other mechanisms associated with the development of fracture.”

In the last decade, the use of bariatric surgery – techniques that either shrink the stomach, or bypass parts of the digestive tract – has increased seven-fold, Huang and his colleagues write in the journal Medicine. Past research has already suggested that the procedure brings an increased risk of bone fractures, they note.

In a national insurance database, the study team identified 2,064 patients who underwent bariatric surgery between 2001 and 2009, and compared them with 5,027 similarly obese patients who did not have the surgeries.

Overall, people who had weight loss surgery had a 21 percent higher risk of breaking a bone in the next five years.

But the added risk was most pronounced among people who underwent “malabsorptive” procedures – the kind that prevent food from being absorbed, such as gastric bypass. They were 47 percent more likely to experience a fracture during 12 years of follow-up compared to those who did not have surgery.

Taking into account whether the bariatric surgery was of this malabsorptive type or just restricted the total amount of food someone could consume at once, such as gastric banding, the researchers found no increase in bone fracture risk among patients who had the restrictive type surgeries.

Bariatric surgeries can reduce and reverse diseases such as type 2 diabetes and hypertension, Huang said. “Therefore, the benefits should outweigh the potential risks if people know how to prevent or decrease the fracture risk.”

The first thing surgical patients should do is take nutrients like vitamin D and calcium supplements, he said.

“Second, sun exposure and exercise can help them from risk for osteoporosis,” Huang said. “Lastly, they should perform some balance training to prevent falls.”

It would be helpful to know more about the patients, such as pre- and post-surgery weight, and supplements they’re taking, said Dr. Andrew Duffy, director of bariatric and metabolic surgery in Connecticut’s Yale-New Haven Health System, who was not involved in the study.

Duffy noted that the fracture increases seen in the study group were mostly in the long bones of the arms and legs, rather than hip or spinal fractures and other types of breaks more typical of osteoporosis.

“They didn’t provide this explanation, but if you are seeing more … leg fractures and stuff in patients that had bariatric surgery, I would argue this might actually be a result of the fact that these patients are exercising more – maybe they had fallen off their bicycles when they are trying to lose weight,” he said.

Duffy said that patients who lose 100 or 200 pounds of weight can also lose diabetes and high blood pressure, and life expectancies in younger patients increase, which is a huge benefit.

He also expects all obesity patients to have some loss of bone mass. “The reason is, if you are 400 pounds and you are walking around, you are going to need more muscle and you need a stronger skeleton to carry that weight.”

If you lose 150 pounds, he said, you are going to lose some bone along with some muscle.

“You obviously don’t want it to be a pathologic thing that’s going to set you up for fractures, which is what this paper in particular is addressing,” he said.

Duffy said that at Yale, and most other programs, doctors do full lab panels to look for vitamin and mineral deficiencies and have their patients take supplements before and after their procedures.